TOPIC: Advice needed on venting sealed bilge

Hope someone out there has some experience with this issue. I am restoring a 1962 Sabre Craft pacer 15. I used floatation foam under the new floor and then glassed and painted over the new plywood. You can see pics in the Gallery section here under 1962 Sabre Craft Pacer 15. Question: do I really need to vent the sealed chamber? Seems like that would just allow moisture in, which could build up over time.

I sealed it all up real good because I just could not see how to get good drainage to the small well at the transom, while, at the same time, letting the foam expand into all the nooks and crannys. No way to go back now so it is either keep it totally sealed, or vent it.

Thanks in advance for any advice on this.

If it were me I would seal it tight, no holes. The '63 Shell Lake I am working on was sealed and after all these years the floor is solid and the stringers are tight. What little water that was in the area came from screw holes that a previous owner didn't seal up after he removed seats and hardware. My Humble Opinion.
Cal

I would say DITTO.

eicoguy,

FIRST, WELCOME ABOARD. - LOTS of experts here to help you with your project.

I hate to so violently disagree with my friends "63 Sabre" & "robert-lorigan", but failing to vent (and perhaps install a fan) the area below the floor is a great way to blow yourself up.
(I seriously doubt that you can throughly seal the bilges.)

Fuel vapors "puddle" under floors (Fuel vapors are heavier than air.), just waiting for a spark/electrical short/whatever to blow someone to Kingdom Come.

IF it was me, I would put several vent holes in the floor (fore and aft), with vent-covers over the holes and would consider a small/cheap blower in one of the vents.

Just my opinion, satx

Me thinks we're talking apples en oranges here. I'm under the impression that you're replacing the fiberglass floor and sealing it so no water can get in. On my woodie (avatar) I have several vents with a blower in the bilge to clear out fuel vapors.
Satx is correct, you can blow a pretty good hole in the water with a vapor mishap but in this case the floor would be filled with floatation and then sealed. Any fuel spillage from your portable tanks would be on top of the floor near your drain plug, right?

Hope you don't mind that I copied your pic from the gallery for reference. She looks like a beauty and a fantastic job!

63 Sabre,

HOW can you be SURE that there are NO leaks for spilled fuel to drip into, just sitting there awaiting a spark/short? How could anyone assure 100% fill of every square inch?
(It takes LITTLE fuel vapor to blow the boat & occupants sky high. Fuel vapor is more explosive by weight than C4.)

Vents are CHEAP insurance.

NOTE: On 24APR65 I SAW an 18' FG runabout explode. - Neither occupant survived.
(More than 4 decades later, I can close my eyes & still see the fireball.)

just my opinion, satx

Well, this is interesting, I thought this was all about moisture and hull expansion/contraction from atmospheric pressure changes.

I never thought of fuel as the issue. I don't see how fuel could possibly get into the space under the floor as it is completely sealed with fiberglass, epoxy and paint. But... wait a minute- that is now, how about 15 or 20 years from now when I am probably dead and gone and my grandchildren are using the boat that old Grandpa left them. The one that now has a few cracks in the floor.

I have certainly considered fuel vapor in terms of not closing off the area under the splash well where the tank will sit. Maybe even one of those little chrome vents on the gunwhale to force air through the that area when under way. But, vapors under the floor - never.

Note that I cannot be absolutely sure that there are no voids in the foam under the floor.

Note also that those grandchildren are the reason I foamed it in the first place.

Spark from what? There's nothing under the floor.

eicoguy,

fwiw, on a HOT day, you can get a "plume" of invisable vapor arising from the under-sole area. - Say maybe a half-cup of the leaked fuel.
Add a spark/electrical short (or someone smoking a cigar) and you have a possible tragedy.
(Truthfully, the exact cause of a vapor explosion is seldom known, as the "evidence" is all over the lake/bay/ocean.)

Most of my 5 decades of experience in "messing about in boats" is "out on the salt" & the pounding from the chop/wave-action can crack fiberglass/wood/etc in as little as 3-5 years.

yours, satx

Reading this thread I think we are all going to have our own ideas on foam flotation and if it should be sealed up or not.I donot want to step on anyone toes here but there are countless ways to look at this one. First off welcome to the site Eicoguy.I looked at your pics and you really seem to have done a great job on your boat so far.Foam has been used in boats for over 50 years now and some have been good and some not so good. First off one thing to remember is that all foam will break down over years of use, some more than others. Gas will eat foam. Gas vapors will only pass through foam. Foam no matter what kind it is will start to absorb water over time. Foam is great for flotation and it does last longer if it is used in a sealed enviroment. It does not matter how well you seal it up, it will absorb fluids at some time in life, be it tomorrow or 50 yrs down the road. As for gas vapors sitting in the bottom of your hull you need to have a reason they are there. Mostly it is from people trying to pour gas into a tank from another tank. Or you have a leaking fuel line or connections. Most fuel leaks are preventable. Having a sealed floor is a great way to prevent a spilled fuel problem to becoming a bigger problem. If a sealed compartment leaks because of cracks in it of other reasons it is up to the owner of that compartment to fix it. If they don't then it is only become a bigger problem. All boats have fuel vapor in them at one time or another during the day. If there is a large amount of vapors present most people have the sense to fix the problem before it can cause other problems. So it is up to you to make your own smart deciesion on if you would seal it up or unsealed. Just remember gas vapor needs an ignition sourse to ignite. As for 40 yrs from now I am pretty sure ther will be more pressing problems with the boat than worry about a crack in the floor that has been there for god knows how long. I say do what makes you happy and your family happy and safe. Remember that proper boat maintanance will keep you safe and happy on the water. Skip.

Skip, Satx, OK, I conceed the venting part but I have to admit it's a real longshot. Always error on the side of safety. Now to get back to the situation at hand, how do you vent a "sealed" vessel? I was thinking of this while reading the responses. Putting a hole in the floor would be out of the question since the whole purpose is to keep water out. Taking a clue from my Sabre there are actual metal vent tubes that run up the inside port and starboard gunwhales(?) It would not be hard to drill 1 1/2" holes in the floor by the sides and run a straight pvc pipe up under the topside. Could be concealed by the seats or something. The pipe/tube would be open on the top and ventilate the bilge area without letting water/gas or whatever get in. The floor area could be sealed with 5200 for a permanent set.
It's an idea I might incorporate in my project now that the idea is there.
If you look at this picture while I was restoring the Sabre you can see the metal vent pipes on the sides, follow the chrome intakes down.

Sabre, you hit the nail on the head there with what is most likely the best vent setup yet.Sealed floor and venting. The best of both worlds. Skip.

Thanks for the input Skip, but know that I am not looking for anyone to make a decision for me. Too old for that for sure. What I am looking for, and getting, is some good advice from those that have much more experience with boating and boat restoration than I. The last boat I owned was one much like this one, but that was 43 years ago. I bought that boat while my wife was in the hospital having twins. Guess what... that didn't work out too well :~) I don't even remember taking that boat out on the water. Far too many other things going on at that time.

63 Sabre,

WOW! - You ought to patent that idea before someone else does, IF it's not already patented. ==========> GREAT IDEA.
(I think that that solves the problem neatly, W/O great cost.)

yours, satx

I'm going to have to camp in the totally sealed, no problem, campsite. Because if it is totally sealed, nothing like gas can get in there. However, I'm thinking our 1938 woody probably needs a better method of venting the bilge.

So I'll wade into the fray. I have done boats a few different ways, two of which are similar to what you are asking about. As a disclaimer I am a big fan of ventilation under the floor and not a big fan of foam but all that said anything done right is OK. Most of the issues we see with old boats are due to workmanship, poor design or poor treatment of the boat. All can be corrected during restoration and during ownership. In general I try to stay true to originality so that limits what I do vs. what I prefer to do.
First off though one thing that has not been brought up is that you cannot totally seal your floor. If there is an air space anywhere this air heats and cools which would raise and lower the static pressure in the area below the floor. This will bulge out and suck in your hull, so in my opinion you need to ventthis space somewhere. Two of my restorations each where originally done with "sealed floors" an MFG Edinboro and a Glasspar G-3. It should be noted despite being "sealed" they each had a drain plug to "drain" the area under the sealed floors. They also both had a small tube, about 3/8 inch diameter up towards the bow that would let the pressure equalize as temperture changed. The tubes where sealed to the floor at the bow and the tube raun up to about gunnel height.
What I did when I restored each was a little different I did the Glasspar G-3 first it was 63 so it had the fiberglass corrogated stringers with no foam and a 1/4 plywood sheet for a floor bonded on top of that. I eliminated the drain plug below the floor, kept the vent tube in the bow and put a 6 inch screw in inspection plate into the floor near the bow on the raised shelf under the front deck. The raised shelf was created because it extended from the foot rest top wo it was sort of a triangular raised area under the front deck. That vent tube vented below this raised area but all the under floor areas were connected.
Were the tube and the inspection plate are up high and towards the front and under the deck I am not worried about significant water entry through these areas. I unscrew the inspection plate tipping the boat bow down and look for any signs of water entry and leave it off to let this area "vent" in case of moisture build up (or possible gas leaking through a crack). This is a 15 year old resto and I have seen no signs of water etc. During winter storage I just leave the inspection plate off. So I guess it's not really sealed but does a good job of preventing water intrusion and gives me a way to keep an eye on things and vent it once in a while.
The MFG was similar except the corrogated stringers where alternately foamed so there were air channels from the under stern area to under the bow area, honestly I'd be happier if it wasn't foamed as mentioned foam will absorb water if allowed, particularly the foam used of this vintage. (yours should be closed cell and a better material) I am well aware of possible advantages of foam and it does make the boat quiet. When I did the transom I was able to check the foam and it was dry, this boat was particularly well treated, the transom rotted out through poor sealing of the motor bolts and unsealed transom top. On this boat I left the vent tube and the underfloor drain plug in place and I added the same inspection plate to the similar foot rest raised area under the deck. I can keep an eye on things and provide ventilating from time to tim. 4 years on this one all is OK.
I am meticulous about any floor penetrations being sealed. I did molded in cleats like yours for the tanks and the battery to minimize fastners.
Another area overlooked is the drain tube, this area is frequently rotted on older boats because water can wick between the tube and the hole it is pressed into, this prevents water from getting in the boat but unseen water can wick into the plywood.Sealants don't work well becasue the tight fit wipe it off during instal. I have a much larger hole in the wood so I cna use thickened epoxy to fill it making a plug of epoxy which I drill a wee bit ovesize and then bond in the tube, this eliminates any wicking to the wood in this area. I do the same for the motor bolt holes and stern eyes. For these I make the hole a wee bigger than the thread diameter and use 5200 to seal it to the epoxy plug.
Looks like you are off to a great restoration there and if deemed fit any of what I have mentioned could be added.
Good luck and thanks for sharing your work.
Randy

Thanks Randy, that sounds like good advice that I can act on. It's too cold to work on the boat now, so whatever I do will have to wait awhile.

Thanks again,
Bill

Randy, great discussion. You answered a puzzeling question I had since I started working on my 63 Shell Lake. In the bow area peak on the raised area there is a small tube molded into that area that sticks up about 3" and the bilge cavity is void, no foam. Maybe that's why the bilge and stringers/floor are not rotted out. A little soft around the floor drain plug that I am cutting out to replace. Thanks for the enlightenment.
Cal
You can see the raised area I am refering to, sounds exactly like yours.

I like the inspection plate idea. Leave them out over winter if you stored out of the weather. The floor in my MFG is open front and back and i take the deck out once every year or so to inspect my wood. Two lag screws and two people can lift the entire deck and seats out in a few minutes.

Not sure where you are, but in NC if you do vent the space under the deck your required to carry an up to date fire exstinguisher. If your going to fasten things down to the deck leaks are almost enevitable. I have yet to see a closed space below the water line that didn't sooner or later end up with water in it.

hitider,

WELCOME ABOARD, tarheel.

fyi, our family owns a beach-house on Oak Island & we spend every January and the first 2 weeks of March there, doing repairs/maintainence.
(The Palermo is rented out to tourists most of the year.)

As for the remainder of your post, you are 100% CORRECT.- Unfortunately, a fire extinguisher does NOT protect a vessel from a vapor explosions but it will be handy for fighting fires.

yours, satx

satx
180 miles of canals in Broward. Looking forward to sunday driving in my new boat project.
Oh yeah USA C/1-504/82ABN

The little copper or plastic line going to the air chamber was only to equalize the pressure difference above and below the sealed area. The line did not vent moisture, at least not enough to make any difference. Putting a pipe into the void to eliminate moisture will likely be of little or no advantage. The elimination of moisture rerquires air movement - and quite a bit of it at that. Because you have foamed the voids, it will be impossible to get air movement in there to remove moisture. The best bet is to have an under - floor bilge drain at the base of the transom. The best way to do this is to put the through hull fitting in before the transom core - and completely embed it in glass or 5200.

But - that is just my take on things.......

Yes, it looks like I have created something of a problem. There is a small well in front of the transom that originally had holes to each side which opened to the underfloor chamber. Any water under the floor would go there and then drain out in a conventional drain through the transom. I can open those back up. With all the foam I'm not sure how effective that's going to be for water, but it would at least provide a vent so far as pressure changes are concerned. So much for a sealed compartment theory. This all sounds worse than it will really be as this boat will be stored inside and never left in the water. Unless I poke a hole in the hull there should not be any water under the floor anyway.

If you decide to put a drain in the sidewall of the sump area, be sure that it is not an open type. It should only be open when you want to inspect for water under there. If you have foamed the void, you don't want any open way for water to get in, as it will be nearly impossible to get the water back out. I probably is best to just leave it sealed up at this point - especially if the boat will be kept out of the weather.

It'll probably be fine & I surely wouldn't loose sleep over it.

Randy had a good point on the "totally sealed" aspect of the floor. My 57 Falls flyer has 3 air chambers. The 2 rear ones are on either side of the motor in the section that curves down to the water behind the transom. The 3rd is under the deck as a foot rest. None were vented from the factory. The rear ones are smaller and the fiberglass if thick and all the surfaces have a healthy curve. The front one is simply a round tube cut to fit the hull along the bottom. Long story short, the non-vented front tank popped the bottom right out from expansion and contraction. When we refinished the boat we had to cut the top of the chamber off and add wood stringers inside of it to bring the bottom flat again. We drilled a 1/16" hole in the tank to let the pressure equalize.

On the flip side, the Larson Sea Lion, has a sealed floor air chamber with a 6" round plexiglass access hole near the center at stern. It also has a drain plug for under the floor. I have not seen a vent tube at the front anywhere like Randy described, and judging from the 'Flyer construction, Larson probably didn't consider expansion and contraction in their designs.

Still, even though a tiny pressure vent hole is necessary on most air chambers, I still choose not to worry about fumes in a, so called, "sealed" air chamber.

Remember the good old days when the auto mechanic would come out to your dad's car, take off the air cleaner and stare into the carburetor with a cigarette hanging off his lower lip and comment, "yep, it's running way to rich." ?

As a follow up at this point I would not drill out your well in the back, just make sure there is not a point of water entry to weep under the floor. I think you are getting a lot of good points to consider on the thread, that's when this site works great.
Me, I would drill small vent hole up front maybe one in front near the the bow through the raised area under the deck, ya gotta let that pressure equalize and sooned than later, reading some of the posts.
I think where you know what the foam looks like under the floor just put the hole where it will vent the most space under the floor. You could even consider more than one hole, just run the tube up high under the deck to eliminate water entry. If you poured foam after the floor was put in and it expanded out everywhere most likely you don't have much air space. If you poured it in and after it cured you did the floor then there probably is a space between the top of the foam and the floor. I might also add that the foam no matter which way you did it will stiffen the bottom....a lot.....to resist any deformation from pressure changes. Still keep in mind a 2 psi difference over even a square foot is almost 300 lbs! (2 psi x 12 in x 12 in = 288 lbs. so it doesn't take much.
I agree these small tubes are for pressure reasons rather than "venting" Again where you know more about what the foam looks like as far as the inspection plate goes your call but it can't hurt and realisticly won't let water in under the floor. Like most of us after obsessing about the restoration the time, effort and money we treat our boats pretty well.
Waiting for Spring here in Massachusetts too! spitting snow, Xmas music on the radio BUT water is open and it's gonna be almost 60 on Monday, which for you southern guys is PLENTY warm enough for your Northern brothers.
Randy
Randy

Ok, now you guys are freaking me out. Just kidding, but I did seal that up when Michigan temps were over 80 degrees and now it is below freezing there. As I sit here in in comfortable sunny Florida I have visions of my boat, back in Michigan, looking like an old guy with his teeth out - you know - jaws all sucked in. I'm headed back Monday and you can guess what the first item is on my to-do list. I'll be drilling those holes for the seat mounting right away. As mentioned here, I'll drill larger holes and fill with epoxy so the actual mounting screws are in the epoxy, not wood.

This website truely is a great source of info and I thank everyone for their contributions to this thread.

Should have mentioned that the seat mounting holes will be left open until a final venting solution is designed.